There was a big campaign on Moparts about 20 years ago with guys doing that very thing, thinning Rusto down like water and rolling 30 coats on a car, sanding each coat, etc. I thought it was way too labor intensive for the $$ saved. But the premise was that you didn't use a paint gun and the neighbors shouldn't be offended. IMO, they were all thinning it way too much.
Here's a door I did back in 2010 with a Harbor Freight paint gun. Some coats of color and some coats of clear - Rusto sold clear in gallon cans back then (maybe they still do?). It is not wetsanded/buffed. I have painted some, but I am not a professional painter.
As a test, I left the door near pine and oak trees behind the house for over a year, it got covered with leaves and snow over the winter. (pic 2, with leaves removed)
Pic 3 is after a cleanup (wash/wax only, still no buffing).
Pic 4 is of an impression of pine needles - but it could've been sanded buffed out.
If it was given a slight amount of protection/love, I am confident it would've lasted for some years.
Some years later I did another experiment on this same door, but with a 4" microfiber roller, and sanded/buffed it afterward. It had tremendous reflection but lots of buffing marks if you caught it at the wrong angle (I'm not a good buffer and didn't have the right micro-polishes).
So my point to all of that - Rustoleum can be a good stop-gap method if a guy doesn't have the $15k to shell out on paint, and needs to get some protection on his car or get it in 1 color for awhile. They also have a lot more color choices than ever before, a guy might find one that's acceptable. And clearcoat is available with their new Turbofan nozzle.
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